When Android MainActivity derives from FormsAppCompatActivity and an Action is double tapped very quickly the app crashes. It doesn't matter if it's a ToolbarItem or a ViewCell.ContextActions MenuItem.
Thrown Exception (Example from https://www.xamarin.com/prebuilt --> Acquaint):
System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index
at System.ThrowHelper.ThrowArgumentOutOfRangeException (System.ExceptionArgument argument, System.ExceptionResource resource) [0x00011] in <ea7cbce7a3ab46cf8715badda3a37739>:0
at System.ThrowHelper.ThrowArgumentOutOfRangeException () [0x00000] in <ea7cbce7a3ab46cf8715badda3a37739>:0
at System.Collections.Generic.List`1[T].get_Item (System.Int32 index) [0x0000c] in <ea7cbce7a3ab46cf8715badda3a37739>:0
at Xamarin.Forms.Application+NavigationImpl+<OnPopModal>d__2.MoveNext () [0x0000d] in C:\BuildAgent\work\aad494dc9bc9783\Xamarin.Forms.Core\Application.cs:302
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in <ea7cbce7a3ab46cf8715badda3a37739>:0
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x0004e] in <ea7cbce7a3ab46cf8715badda3a37739>:0
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x0002e] in <ea7cbce7a3ab46cf8715badda3a37739>:0
at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x0000b] in <ea7cbce7a3ab46cf8715badda3a37739>:0
at System.Runtime.CompilerServices.TaskAwaiter`1[TResult].GetResult () [0x00000] in <ea7cbce7a3ab46cf8715badda3a37739>:0
at Acquaint.XForms.BaseNavigationViewModel+<PopModalAsync>c__async4.MoveNext () [0x00046] in /Users/username/Downloads/app-acquaint-master 2/App/Acquaint.XForms/Acquaint.XForms/ViewModels/BaseNavigationViewModel.cs:57
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in <ea7cbce7a3ab46cf8715badda3a37739>:0
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x0004e] in <ea7cbce7a3ab46cf8715badda3a37739>:0
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x0002e] in <ea7cbce7a3ab46cf8715badda3a37739>:0
at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x0000b] in <ea7cbce7a3ab46cf8715badda3a37739>:0
at System.Runtime.CompilerServices.TaskAwaiter`1[TResult].GetResult () [0x00000] in <ea7cbce7a3ab46cf8715badda3a37739>:0
at Acquaint.XForms.SettingsViewModel+<ExecuteSaveCommand>c__async1.MoveNext () [0x0021a] in /Users/username/Downloads/app-acquaint-master 2/App/Acquaint.XForms/Acquaint.XForms/ViewModels/SettingsViewModel.cs:141
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in <ea7cbce7a3ab46cf8715badda3a37739>:0
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x0004e] in <ea7cbce7a3ab46cf8715badda3a37739>:0
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x0002e] in <ea7cbce7a3ab46cf8715badda3a37739>:0
at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x0000b] in <ea7cbce7a3ab46cf8715badda3a37739>:0
at System.Runtime.CompilerServices.TaskAwaiter.GetResult () [0x00000] in <ea7cbce7a3ab46cf8715badda3a37739>:0
at Acquaint.XForms.SettingsViewModel+<>c__async5.MoveNext () [0x00021] in /Users/username/Downloads/app-acquaint-master 2/App/Acquaint.XForms/Acquaint.XForms/ViewModels/SettingsViewModel.cs:53
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in <ea7cbce7a3ab46cf8715badda3a37739>:0
at System.Runtime.CompilerServices.AsyncMethodBuilderCore.<ThrowAsync>m__0 (System.Object state) [0x00000] in <ea7cbce7a3ab46cf8715badda3a37739>:0
at Android.App.SyncContext+<Post>c__AnonStorey0.<>m__0 () [0x00000] in <de8603109e284ddbb9bdf88cbec24e9f>:0
at Java.Lang.Thread+RunnableImplementor.Run () [0x0000b] in <de8603109e284ddbb9bdf88cbec24e9f>:0
at Java.Lang.IRunnableInvoker.n_Run (System.IntPtr jnienv, System.IntPtr native__this) [0x00009] in <de8603109e284ddbb9bdf88cbec24e9f>:0
at at (wrapper dynamic-method) System.Object:b2e090dc-1b4e-47d1-82de-b358633bc0d8 (intptr,intptr)

Thank you for submitting this report! Please include the following to help us begin investigation:
1. Minimized runnable test case demonstrating the issue
2. Steps to reproduce
3. Full version information from Xamarin Studio > About Xamarin Studio > Show Details > Copy Information [button]
Thank you,
Xamarin Support

@lars @ Dmitijs Jesilevskis
Could you test with Xamarin.Forms 2.3.3.163-pre3?
I am still unable to reproduce a crash on device, but finally reproduced with the original test case as-is and an accelerated emulator (x86, API 23).
However, after updating to Xamarin.Forms 2.3.3.163-pre3, I am unable to reproduce a crash on emulator or device.
### Results
System.NullReferenceException: Object reference not set to an instance of an object.
at Xamarin.Forms.Platform.Android.CellAdapter.OnActionItemClickedImpl (Android.Views.IMenuItem item) [0x00007] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\CellAdapter.cs:253
at Xamarin.Forms.Platform.Android.CellAdapter.global::Android.Support.V7.View.ActionMode.ICallback.OnActionItemClicked (Android.Support.V7.View.ActionMode mode, Android.Views.IMenuItem item) [0x00000] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\CellAdapter.cs:90
at Android.Support.V7.View.ActionMode+ICallbackInvoker.n_OnActionItemClicked_Landroid_support_v7_view_ActionMode_Landroid_view_MenuItem_ (System.IntPtr jnienv, System.IntPtr native__this, System.IntPtr native_mode, System.IntPtr native_item) [0x00019] in <c690702816034f28aca512af1f0abd66>:0
at at (wrapper dynamic-method) System.Object:856f457d-3c6f-4ed6-854a-78fc22d118f2 (intptr,intptr,intptr,intptr)
### Application Output & adb logcat logs
https://microsoft-my.sharepoint.com/personal/asgazi_microsoft_com/_layouts/15/guestaccess.aspx?guestaccesstoken=2%2f%2fSncer7c1PktV7js2%2bO6vIjkQ0KUD6q2Et1%2fnGYzg%3d&folderid=2_1b9021b1b00264558996e3e9afdb10531&rev=1